In general, a polyimide(hereinafter referred to as "PI") resin denotes a high heat-resistant resin which is manufactured by condensation polymerization of aromatic tetracarboxylic acid or the derivatives thereof with aromatic diamine, or aromatic diisocyanate followed by imidization. However, the PI resin is insoluble in solvent and non-meltable by heat.
Further, the PI resin can have a variety of molecular structures depending on the types of the monomers thereof. As for the aromatic tetracarboxylic acid constituent, pyromellitic dianhydride(PMDA) or biphenyltetracarboxylic dianhydride(BPDA) are used herein. As for the aromatic diamine constituent, oxydianiline(ODA) or p-phenylene diamine(p-PDA) are used for condensation polymerization. The typical PI resin has a repetitive unit of the following formula 10: ##STR8##
The PI resin with the formula 10 as repetitive unit is high heat-resistant, insoluble, and non-meltable with the following properties:
(1) excellent heat-resistance oxidation property; PA1 (2) superior heat-resistance based on the utilization at high temperature, i.e., 260.degree. C. for a long-term use, and 480.degree. C. for a short-term use; PA1 (3) excellent electrochemical and mechanical properties; PA1 (4) excellent radiation resistance and low temperature properties; PA1 (5) intrinsic non-combustible properties; and, PA1 (6) excellent chemicals-resistant properties.
In spite of the fact that the PI resin with formula 10 as repetitive unit possesses an excellent heat resistance property, the processing therein is extremely difficult due to insolubility and non-melting property.
To overcome the shortcomings of the PI resin, several methods have been devised: a) method of introducing polar groups into the backbone or side chains of the polymer, b) method of introducing the connecting groups or pendant groups with a large volume into the polymer, and c) method of enhancing the flexibility of the backbone of the polymer.
In particular, as part of research to enhance the solubility of the PI resin, T. Kurosaki et al. reported a method of preparing a soluble PI using alicyclic anhydride as a monomer(Macromolecules, 1994, 27, 1117 and 1993, 26, 4961). Also, Qn Jin et al. disclosed in 1993 a method of preparing a soluble PI resin using the cyclic diamine(J.P.S. Part A. Polym. Chem. Ed., 31, 2345.about.2351).
In the present invention, the mixture of dioxotetrahydrofuryl 3-methylcyclohexene-1,2-dicarboxylic dianhydride(DOCDA) and aromatic tetracarboxylic dianhydride for the carboxylic acid constituent to prepare the novel soluble polyimides was used. The mixture therefrom undergoes poly-condensation reaction with the mixture of 3,5-diaminobenzamide derivatives having various side chain and the conventional aromatic diamines. Using the process as above, the invention herein has been so devised.
Consequently, the invention herein has a superior heat-resistance, optical transparency, solubility, processability while maintaining the basic characteristics of the conventional PI. As such, the invention herein can be used as core heat-resistance material in the advanced electronics and aerospace industries. Further, the objective of the invention lies in providing a novel PI resin having a liquid crystal alignment property for the application of TFT-LCD liquid crystal alignment layer.